Some compression-molded composites combine a light-weight, low-density core with fiber-reinforced thermoplastic skins or outer layers thereby resulting in a sandwich structure. The resulting composite component has a high stiffness-to-weight ratio thereby making it desirable for use in a wide variety of applications including load-bearing applications. In general, the thicker the core, the higher the load-bearing capacity of the composite component.
As a result of their high stiffness-to-weight ratio and load-bearing capacity, such compression-molded composites have been used as load floors in automotive applications and as skis or snowboards (i.e, sliding boards) in recreational applications.
The prior art discloses a method of making a panel of sandwich-type composite structure having a cellular core in a single processing step. In that method, the panel is made by subjecting a stack of layers of material to cold-pressing in a mold. As shown in FIG. 1, the stack is made up of: at least a first skin made of a stampable reinforced thermoplastics material, a cellular core made of a thermoplastics material, and a second skin also made of a stampable reinforced thermoplastics material. The stack may also include one or more external covering layers made of a woven or non-woven thermoplastic material. The skins are typically pre-heated outside the mold to a softening temperature.
Such a method is particularly advantageous because of the fact that it makes it possible, in a single operation, to generate cohesion and bonding between the various layers of the composite structure as shown in FIG. 2, and to shape the resulting panel while preserving all of the mechanical properties imparted by the cellular-core sandwich structure.
Panels of sandwich-type composition structure having a cellular core have rigidity characteristics sufficient to enable mechanical structures subjected to large stresses to be reinforced structurally without making them too heavy. Such panels are in common use in shipbuilding, aircraft construction, and rail vehicle construction.
The following U.S. patent documents are related to the present invention: U.S. Pat. Nos. 7,419,713; 6,890,023; 6,843,525; 6,537,413; 6,050,630; and 2005/0189674.
One problem associated with such composites is that their function and design freedom is limited by their designed material thickness.
Other U.S. patent documents related to the present invention include: U.S. Pat. Nos. 5,502,930; 5,915,445; 6,102,464; 6,435,577; 6,655,299; 6,682,675; 6,748,876; 6,790,026; 6,682,676; 6,823,803; 6,981,863; 7,090,274; 7,909,379; 7,919,031; 8,117,972; 2006/0255611; and 2008/0185866.
Another problem associated with the prior art is that it is often not desirable to increase the thickness of the core in order to increase the load bearing capacity of the composite component. Increasing the thickness of the core reduces the amount of available space in which the component is located. For example, in a vehicle, the amount of space available for storage is typically quite limited. By reducing the thickness of the core, the amount of available space useful for storage can be increased substantially especially if such components cover a relatively large surface area. One possible solution to the above problem is to provide additional supports at the underside of the component. However, this adds additional cost and weight to the component as well as taking away valuable storage space due to the increased thickness of the resulting component.